The era surrounding World War II was such a rich period of history that it's no wonder many facts simply slipped under the radar, only to be discovered by historians decades later.

The story of the FUSAG is one which escaped the mainstream annals of history, due in part to the secretive nature of the operation.

Known as the Ghost Army, the FUSAG was a phantom Army Group used to draw the Nazis off the trail of other invasion plans which had been set into motion.

Here's more on the ultimate bluff:

The Allied intelligence services created two fake armies to keep the Germans on their toes. One would be based in Scotland for a supposed invasion of Norway and the other headquartered in southeast England to threaten the Pas-de-Calais.

The northern operation relied mainly on fake radio traffic and the feeding of false information to double agents to create the impression of a substantial army. Fortitude South, though, was well within the range of prying German ears and eyes, so fake chatter alone would be uncovered too quickly.

The Allies would have to make it look and sound like a substantial army was building up in southeast England. They needed boots on the ground there, without actually using too much of their precious manpower.

When intelligence officers learned that the First U.S. Army Group (FUSAG) was to be redesignated the 12th Army Group, they knew they had their Pas-de-Calais invaders. The FUSAG was kept alive on paper, and the phantom army was given a few real soldiers and placed under the command of one of the era’s great military leaders.

Want to know more? Head over to Mental Floss and read the entire article by Matt Soniak to get the whole scoop on the ultimate wartime fake out.